Remove blue border header class

The header is already blue by default, so adding a blue border doesn't
make a noticeable visual difference. This commit removes the
app-header--blue CSS class and tweaks the component logic to stop it
being added.

Author: DavidBiddle

app/components/header_component/_index.scss

@@ -23,8 +23,4 @@
   &.app-header--yellow {
     border-bottom: 10px solid govuk-colour("yellow");
   }
-
-  &.app-header--blue {
-    border-bottom: 10px solid govuk-colour("blue");
-  }
 }

app/components/header_component/view.rb

@@ -14,6 +14,8 @@ def environment_name
     end
 
     def app_header_class_for_environment
+      return nil if colour_for_environment == "blue"
+
       "app-header--#{colour_for_environment}"
     end
 

spec/components/header_component/view_spec.rb

@@ -60,7 +60,6 @@
       { colour: "pink" },
       { colour: "green" },
       { colour: "yellow" },
-      { colour: "blue" },
     ].each do |scenario|
       context "when colour_for_environment is #{scenario[:colour]}" do
         before do
@@ -72,6 +71,16 @@
         end
       end
     end
+
+    context "when colour_for_environment is blue" do
+      before do
+        allow(header_component).to receive(:colour_for_environment).and_return("blue")
+      end
+
+      it "returns nil because the header is already blue" do
+        expect(header_component.app_header_class_for_environment).to be_nil
+      end
+    end
   end
 
   describe "#colour_for_environment" do